J Comp Physiol A (1991) 168:103-112 Journal of Nml, mad I r ioloWl A 9 Springer-Verlag 1991 Different effects of the biogenic amines dopamine, serotonin and octopamine on the thoracic and abdominal portions of the escape circuit in the cockroach Ronald S. Goldstein* and Jeffrey M. Camhi** Neurobehavior Unit, Department Zoology, Hebrew University, Jerusalem, Israel Accepted August 20, 1990 Summary. 1. The escape behavior of the cockroach, Peri- planeta americana, is known to be modulated under vari- ous behavioral conditions (Camhi and Volman 1978; Camhi and Nolen 1981; Camhi 1988). Some of these modulatory effects occur in the last abdominal ganglion (Daley and Delcomyn 198 la, b; Libersat et al. 1989) and others in the thoracic ganglia (Camhi 1988). Neuro- modulator substances are known to underlie behavioral modulation in various animals. Therefore, we have sought to determine whether topical application of puta- tive neuromodulators of the escape circuit enhance or depress this circuit, and whether these effects differ in the last abdominal vs. the thoracic ganglia. 2. Topical application of the biogenic amines serotonin and dopamine to the metathoracic ganglion modulates the escape circuitry within this ganglion; serotonin decreases and dopamine enhances the response of leg motoneurons to activation of interneurons in the abdominal nerve cord by electrical or wind stimulation (Figs. 2-7). 3. The neuropil of the thoracic ganglia contains many catecholamine-histofluorescent processes bearing vari- cosities, providing a possible anatomical substrate for dopamine release sites (Fig. 8). 4. Topical application of octopamine to the termi- nal abdominal ganglion enhances the response of ab- dominal interneurons to wind stimulation of the cerci (Figs. 10, 11). In contrast, serotonin and dopamine have no effect at this site (Figs. 9, 11). 5. It is proposed that release of these biogenic amines may contribute to the known modulation of the cock- roach escape response. Key words: Biogenic amines - Neuromodulation - Insect CNS - Giant interneurons Abbreviations: GI abdominal giant interneuron ; TI thoracic giant interneuron; 5-HT 5-hydroxytryptamine(serotonin); CNS central nervous system * Present adress: Department of Anatomy and Embryology, Hadassah Medical school, Hebrew University-Ein Karem, Jerusalem, Israel ** To whom offprint requests should be adressed Introduction Certain neuroactive substances increase or decrease the activity of populations of neurons and can markedly modify the expression of behaviors. Substances with these properties have been termed neuromodulators (Kupfermann 1979). Experimentally, these effects can be elicited by application of the neuromodulatory sub- stances to neural tissue or by activation of identified neurons containing the substances. Systems that are par- ticularly suitable for studying the effects of neuro- modulatory substances are those in which: 1) The neural circuit is well worked out in terms of individually iden- tified neurons and their connections; and 2) the behavior that this circuit controls varies naturally under different circumstances, in ways that can be quantified. One system that meets both these criteria, and yet about which very little is known concerning the role of neuromodulators, is the cockroach escape circuit - the subject of the present study. A puff of wind directed at this animal results in a turn almost always away from the wind source, followed by brisk running (Camhi and Tom 1978). This stimulus simulates the air movement provided by the approach of a natural predator, and constitutes the cockroach's major means of escaping from large, approaching predators (Camhi et al. 1978). The neural circuit underlying the escape turn includes over 200 wind receptors on each of two abdominal sense organs called cerci. Their axons project to the 6th, or last abdominal ganglion (A6), where they excite seven bilat- eral pairs of giant interneurons (GIs), among other cells (Westin et al. 1977). The GI axons ascend the entire nerve cord (Spira et al. 1971). In passing through the thoracic ganglia, they excite a group of thoracic interneurons (TIs) that in turn excite the leg motor neurons (Ritzmann and Pollack 1988). Thus, there are two major neural integration centers that are well separated and accessible for study, ganglion A6 and the thoracic ganglia. In this study we focus on A6 and the metathoracic, or 3rd thoracic ganglion T3. The cockroach escape behavior is modulated under several different behavioral conditions. For instance,